An outboard motor powered by an internal combustion engine is usually mounted directly on a transom at the stern of a boat, and is oftentimes covered with splashes of water during operation of the boat. In order to protect the internal combustion engine from splashes of water, the engine is typically enclosed in an engine cover (See for example U.S. Pat. No. 4,698,037).
The internal combustion engine requires air for combustion, and therefore the engine cover must be provided with an air intake for introducing air to the engine. This makes it practically impossible to completely prevent ingress of water into the engine compartment.
In order to discharge water from the engine compartment, it has been conventionally known to provide a drain aperture in the bottom plate of the engine compartment. However, such a drain aperture itself may permit ingress of water into the engine compartment for example when the outboard motor is totally or partially submerged during heavy wave conditions. Such ingress of water from the drain aperture can damage electric components mounted in the engine compartment. Although some conventional drain systems are designed so as to prevent water from entering the engine compartment (See for example U.S. Pat. No. 4,758,190), they had complicated configurations and were difficult to assemble.